Positioning using observer-based time-of-arrival measurements

ABSTRACT

A method of determining a position of a target device includes: sending a first measurement signal from a first known-position device; receiving the first measurement signal at a second known-position device; receiving a first acknowledgement signal from the target device at the first known-position device and at the second known-position device; determining the position of the target device using first timing information associated with the first measurement signal and the first acknowledgement signal, a first position of the first known-position device, and a second position of the second known-position device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/683,182, filed Aug. 14, 2012, entitled “SYSTEM RECIPE FOR OBSERVER BASED TOA MEASUREMENTS,” that is assigned to the assignee hereof and is incorporated herein by reference for all purposes.

BACKGROUND

It is often desired to know or determine the location of a device in a network such as a wireless local area network (WLAN). Various techniques for determining location in a WLAN presently exist. For example, a communication may be sent from a first device to a second device that then sends an acknowledgement message back to the first device. The round-trip time (RTT) from the sending of the communication to the receipt of the acknowledgement may be used to determine the distance (which may be an estimated distance) from the second device to the first device, from which location information for the second device may be determined The RTT, however, includes turnaround time used by the second device to process the communication and send the acknowledgement. If this turnaround time varies, then the determined distance from the second device to the first device will vary.

Referring to FIGS. 1A-1B, a system for determining RTT includes an access point and a mobile device. At a first time, the access point sends Packet 1 to the mobile device that responds by sending an acknowledgement signal ACK 1 to the access point. At a second time, Packet 2 is sent to the mobile device that returns an acknowledgement signal ACK 2 to the access point. An RTT from a time that a packet is sent from a media access control (MAC) of the access point to a time that the acknowledgement reaches the MAC can be determined according to:

RX′=RX+MP+CSD   (1)

In equation (1), RX is the ideal receive delay, of the acknowledgement, incurred from the antenna of the access point to the MAC of the access point if a cabled signal were presented at the antenna free of multipath and cyclic shift delay (CSD), MP is a timing error attributable to multipath in the receive path, and CSD is the timing error in receiving the acknowledgement by the access point attributable to the cyclic shift delay present at the transmitter of the acknowledgement. RX′ represents the sum of actual delay and timing errors incurred in the scenario of over-the-air reception of the packet in the presence of real multipath and CSD error terms.

SUMMARY

An example method of determining a position of a target device includes: sending a first measurement signal from a first known-position device; receiving the first measurement signal at a second known-position device; receiving a first acknowledgement signal from the target device at the first known-position device and at the second known-position device; determining the position of the target device using first timing information associated with the first measurement signal and the first acknowledgement signal, a first position of the first known-position device, and a second position of the second known-position device.

Implementations of such a method may include one or more of the following features. The first timing information comprises a transmission time of the first measurement signal, a first time of arrival of the first acknowledgement signal in the first known-position device, a second time of arrival of the first measurement signal in the second known-position device, and a third time of arrival of the first acknowledgement signal in the second known-position device, and using the first timing information comprises determining a first distance and a second distance from the target device to the first known-position device and the second known-position device, respectively, using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival. Using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival comprises determining a difference between (1) a difference between the first time of arrival and the transmission time and (2) a difference between the third time of arrival and the second time of arrival. The method further includes: receiving the first measurement signal at a third known-position device; and receiving the first acknowledgement signal from the target device at the third known-position device; where the first timing information comprises a transmission time of the first measurement signal, a first time of arrival of the first acknowledgement signal in the first known-position device, a fourth time of arrival of the first measurement signal in the third known-position device, and a fifth time of arrival of the first acknowledgement signal in the third known-position device; and using the first timing information comprises determining a third distance from the target device to the third known-position device using the fourth time of arrival and the fifth time of arrival.

Also or alternatively, implementations of such a method may include one or more of the following features. The method further includes: sending a second measurement signal from the second known-position device; receiving the second measurement signal at the first known-position device; and receiving a second acknowledgement signal from the target device at the first known-position device and at the second known-position device; where determining the position of the target device further comprises using second timing information associated with the second measurement signal and the second acknowledgement signal. The method further includes sending an exchange message from the first known-position device indicating receipt of the first acknowledgement signal, where the second measurement signal is sent from the second known-position device in response to the exchange message being received by the second known-position device. The first known-position device and the second known-position device form a measurement-observer known-position device pair, and the method further includes obtaining further timing information from further measurement-observer known-position device pairs for the target device, where determining the position of the target device further comprises using the further timing information to determine the position of the target device using trilateration.

An example apparatus for determining a position of a target device includes: a network interface; a control engine communicatively coupled to the network interface and configured to: send, via the network interface, a first instruction to a first network device to act as a measurement network device to send a first measurement signal; and send, via the network interface, a second instruction to a second network device to act as an observer network device to receive the first measurement signal, the first network device having a first known position and the second network device having a second known position; and a position engine, communicatively coupled to the control engine and the network interface, configured to: receive, via the network interface, first timing information associated with the first measurement signal; and determine a position of the target device based on the first timing information, the first known position, and the second known position.

Implementations of such an apparatus method may include one or more of the following features. The first timing information comprises: a transmission time of the first measurement signal; a first time of arrival in the first network device of a first acknowledgement signal sent by the target device in response to receiving the first measurement signal; a second time of arrival of the first measurement signal in the second network device; and a third time of arrival of the first acknowledgement signal in the second network device, and the position engine, to determine the position of the target device, is configured to determine a first distance and a second distance from the target device to the first network device and the second network device, respectively, using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival. Using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival comprises determining a difference between (1) a difference between the first time of arrival and the transmission time and (2) a difference between the third time of arrival and the second time of arrival. The control engine is further configured to instruct a third network device to act as another observer network device, the third network device having a third known position, the first timing information further comprises: a fourth time of arrival of the first measurement signal in the third network device; and a fifth time of arrival of the first acknowledgement signal in the third network device, and the position engine, to determine the position of the target device, is further configured to determine a third distance from the target device to the third network device using the fourth time of arrival and the fifth time of arrival. The control engine is further configured to instruct the first network device to act as the observer network device and the second network device to act as the measurement network device, and the position engine is further configured to: receive, via the network interface, second timing information associated with a second measurement signal sent from the second network device and received by the first network device while acting as the observer network device; and determine the position of the target device further based on the second timing information.

Another example apparatus for determining a position of a target device includes: a network interface; control means, communicatively coupled to the network interface, for: sending, via the network interface, a first instruction to a first network device to act as a measurement network device to send a first measurement signal; and sending, via the network interface, a second instruction to a second network device to act as an observer network device to receive the first measurement signal, the first network device having a first known position and the second network device having a second known position; and position determining means, communicatively coupled to the control means and the network interface, for: receiving, via the network interface, first timing information associated with the first measurement signal; and determining a position of the target device based on the first timing information, the first known position, and the second known position.

Implementations of such an apparatus may include one or more of the following features. The first timing information comprises: a transmission time of the first measurement signal; a first time of arrival in the first network device of a first acknowledgement signal sent by the target device in response to receiving the first measurement signal; a second time of arrival of the first measurement signal in the second network device; and a third time of arrival of the first acknowledgement signal in the second network device, and the position determining means, for determining the position of the target device, is configured to determine a first distance and a second distance from the target device to the first network device and the second network device, respectively, using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival. Using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival comprises determining a difference between (1) a difference between the first time of arrival and the transmission time and (2) a difference between the third time of arrival and the second time of arrival. The control means is further for instructing a third network device to act as another observer network device, the third network device having a third known position, the first timing information further comprises: a fourth time of arrival of the first measurement signal in the third network device; and a fifth time of arrival of the first acknowledgement signal in the third network device, and the position determining means, for determining the position of the target device, is further configured to determine a third distance from the target device to the third network device using the fourth time of arrival and the fifth time of arrival. The control means is further configured to instruct the first network device to act as the observer network device and the second network device to act as the measurement network device, and the position determining means is further for: receiving, via the network interface, second timing information associated with a second measurement signal sent from the second network device and received by the first network device while acting as the observer network device; and determining the position of the target device further based on the second timing information.

An example processor-readable storage medium includes processor-readable instructions configured to cause a processor to: send a first instruction to a first network device to act as a measurement network device to send a first measurement signal; send a second instruction to a second network device to act as an observer network device to receive the first measurement signal, the first network device having a first known position and the second network device having a second known position; receive first timing information associated with the first measurement signal; and determine a position of the target device based on first timing information, the first known position, and the second known position; where the first timing information is associated with the first measurement signal.

Implementations of such a storage medium may include one or more of the following features. The first timing information comprises: a transmission time of the first measurement signal; a first time of arrival in the first network device of a first acknowledgement signal sent by the target device in response to receiving the first measurement signal; a second time of arrival of the first measurement signal in the second network device; and a third time of arrival of the first acknowledgement signal in the second network device, and the instructions configured to cause the processor to determine the position of the target device are configured to cause the processor to determine a first distance and a second distance from the target device to the first network device and the second network device, respectively, using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival. Using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival comprises determining a difference between (1) a difference between the first time of arrival and the transmission time and (2) a difference between the third time of arrival and the second time of arrival. The instructions further comprise instructions configured to cause the processor to instruct a third network device to act as another observer network device, the third network device having a third known position, the first timing information further comprises: a fourth time of arrival of the first measurement signal in the third network device; and a fifth time of arrival of the first acknowledgement signal in the third network device, and the instructions configured to cause the processor to determine the position of the target device are configured to cause the processor to determine a third distance from the target device to the third network device using the fourth time of arrival and the fifth time of arrival. The processor-readable storage medium further includes instructions configured to cause the processor to instruct the first network device to act as the observer network device and the second network device to act as the measurement network device, where the instructions configured to cause the processor to determine the position of the target device are configured to cause the processor to: receive, via the network interface, second timing information associated with a second measurement signal sent from the second network device and received by the first network device while acting as the observer network device; and determine the position of the target device further based on the second timing information.

Another example method of determining a position of a target device includes: sending a first instruction to a first network device to act as a measurement network device to send a first measurement signal; sending a second instruction to a second network device to act as an observer network device to receive the first measurement signal, the first network device having a first known position and the second network device having a second known position; receiving first timing information associated with the first measurement signal; and determining the position of the target device based on the first timing information, the first known position, and the second known position.

Implementations of such a method may include one or more of the following features. The first timing information comprises: a transmission time of the first measurement signal; a first time of arrival in the first network device of a first acknowledgement signal sent by the target device in response to receiving the first measurement signal; a second time of arrival of the first measurement signal in the second network device; and a third time of arrival of the first acknowledgement signal in the second network device, and determining the position of the target device comprises determining a first distance and a second distance from the target device to the first network device and the second network device, respectively, using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival. Using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival comprises determining a difference between (1) a difference between the first time of arrival and the transmission time and (2) a difference between the third time of arrival and the second time of arrival. The method further includes instructing a third network device to act as another observer network device, the third network device having a third known position, where the first timing information further comprises: a fourth time of arrival of the first measurement signal in the third network device; and a fifth time of arrival of a first acknowledgement signal in the third network device, and where determining the position of the target device comprises determining a third distance from the target device to the third network device using the fourth time of arrival and the fifth time of arrival. The method further includes: instructing the first network device to act as the observer network device and the second network device to act as the measurement network device; and receiving second timing information associated with a second measurement signal sent from the second network device and received by the first network device while acting as the observer network device, where determining the position of the target device is further based on the second timing information.

Items and/or techniques discussed herein may provide one or more of the following capabilities, as well as other capabilities not mentioned. Power consumption for location determination may be reduced, e.g., by reducing the amounts of packets exchanged, compared to present location techniques. System capacity for communication systems that implement device (e.g., mobile device) location determination may be increased, e.g., by reducing the amounts of packets exchanged, compared to present systems. Reliable location determination may be provided for devices that use software media access controllers. Error in device location determination may be reduced by having a tightly constrained fit (e.g., a three-point fit based on a three distance measurements) for a difference between transmission times of signals between a device with an unknown location/position and devices (e.g., access points) with known locations/positions. Location determination error due to variable turnaround time may be reduced or even eliminated. Error in device location determination may be reduced by eliminating dependence on knowledge of device processing times (e.g., turnaround time and signal receiving transfer time from antenna to MAC). Error in device location determination due to cyclic shift delay (CSD) and multipath for signals received at a measuring device may be reduced. Other capabilities may be provided and not every implementation according to the disclosure must provide any, let alone all, of the capabilities discussed. Further, it may be possible for an effect noted above to be achieved by means other than that noted, and a noted item/technique may not necessarily yield the noted effect.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIGS. 1A-1B are block diagrams of prior art round-trip time measurements.

FIG. 2 is a schematic diagram of a communication system.

FIG. 3 is a block diagram of a mobile station shown in FIG. 2.

FIG. 4 is a block diagram of a network device shown in FIG. 2.

FIG. 5 is a block diagram of a server shown in FIG. 2.

FIG. 6 is a partially functional block diagram of network devices shown in FIG. 2.

FIG. 7 is a partially functional block diagram of the server shown in FIG. 2.

FIGS. 8-10 are block flow diagrams processes of determining a position of the target device.

FIG. 11 is a schematic diagram of timing measurements between network devices.

FIG. 12 is a schematic diagram of a timing measurements in combination of devices for locating a target device.

FIG. 13 is a block flow diagram of a method of determining a position of a target device.

DETAILED DESCRIPTION

Using techniques discussed herein, an observer network device can be used in combination with a measurement network device to determine location of another network device. For example, a measurement signal is sent from a measurement access point to an observer access point and to a mobile device. The mobile device responds to the measurement signal by sending an acknowledgement signal to the measurement access point and to the observer access point. Times-of-arrival of the measurement signal at the observer access point and the acknowledgement signal at the measurement access point and the observer access point, and a time of transmission of the measurement signal are used to determine a position of the mobile device. The measurement and observer access points can change roles and take further measurements. Further, multiple access point measurement-observer pairs may be used to obtain measurements for use in determining the position of the mobile device. Other implementations may be used. For example, while the example discussed above, and the examples discussed below focus on mobile devices and access points, devices other than mobile devices and/or access points may be used and the techniques discussed herein are applicable to any types of devices having the functionality discussed. Further, a measurement signal may be received and processed by multiple observer devices concurrently and a position of a position of a device of unknown position may be determined using information from the multiple observer devices, perhaps without further measurements.

Referring to FIG. 2, a communication system 10 includes network devices 12, 14, 16, a network 18, and a server 19. As an example, in FIG. 2 the network device 12 is shown as a mobile station (MS) 12, the network devices 14 are shown as access points (APs) 14, and the network device 16 is shown as a base transceiver station (BTS) 16. While APs are typically associated with wireless local area networks (WLANs) and BTSs are typically associated with wireless wide area network (WWANs), the terms AP and BTS are used herein generically as being applicable to WLANs or WWANs as the network devices 14, 16 could be configured for operation in either or both types of networks, and are shown in FIG. 2 as APs and a BTS as an example only. The system 10 is a communication system in that the system 10 can at least send and receive communications between the BTS 16 and the APs 14, between the BTS 16 and the MS 12, between the APs 14 and the MS 12, between the BTS 16 and the network 18, between the APs 14 and the network 18, and between the network 18 and the server 19. Only one MS 12 is shown, but more than one MS 12 will typically be present and the system 10 is configured to support numerous MSs 12 concurrently.

The BTS 16 can wirelessly communicate with the APs 14 via antennas. The BTS 16 may also be referred to as a base transceiver station, an access node (AN), a Node B, an evolved Node B (eNB), etc.

The MS 12 can be moved to various locations, including into buildings and onto different floors of the buildings. The MS 12 may be referred to as an access terminal (AT), a mobile device, user equipment (UE), or a subscriber unit. The MS 12 is shown here as a cellular phone. Other examples of MSs include wireless routers, personal digital assistants (PDAs), netbooks, notebook computers, tablet computers, etc. Only one MS 12 is shown in FIG. 2, and to simplify the discussion below only this MS 12 is discussed.

The APs 14 can be moved to various locations. Pairs of the APs 14, e.g., the AP 14 ₁ and the AP 14 ₂ are used to measure time of arrival (TOA), with one of the APs 14, e.g., the AP 14 ₁, being an observer AP and the other AP 14, e.g., the AP 14 ₂, being a measurement AP as discussed below.

Referring to FIG. 3, an example of the MS 12 comprises a computer system including a processor 20, memory 22 including software 24, transmitters 26, antennas 28, and receivers 30. The transmitters 26, antennas 28, and receivers 30 form a wireless communication module that can communicate with the APs 14. The transmitters 26 and receivers 30 are configured to communicate bi-directionally with the APs 14 via the antennas 28. The processor 20 is preferably an intelligent hardware device, e.g., a central processing unit (CPU) such as those made by ARM®, Intel® Corporation, or AMD®, a microcontroller, an application specific integrated circuit (ASIC), etc. The processor 20 could comprise multiple separate physical entities that can be distributed in the MS 12. The memory 22 is a processor-readable storage medium that includes random access memory (RAM) and read-only memory (ROM). The memory 22 stores the software 24 which is processor-readable, processor-executable software code containing processor-readable instructions that are configured to, when executed, cause the processor 20 to perform various functions described herein. Alternatively, the software 24 may not be directly executable by the processor 20 but configured to cause the processor 20, e.g., when compiled and executed, to perform the functions.

The MS 12 may be configured with any of a variety of media access control (MAC) types. For example, the MS 12 may have a hardware MAC, a firmware assisted MAC, or a software MAC. Hardware MACs typically provide consistent turnaround times (to receive a packet and send an acknowledgement) of about 1-2 clock cycle. Firmware assisted MACs typically provide slightly variable turnaround times of about 10-20 clock cycles. Software MACs typically provide highly variable turnaround times of over 20 clock cycles. The techniques discussed below may be used with the MS 12 having any such MAC. MAC, as used herein, refers to MAC-layer signal processing.

Referring to FIG. 4, an example of one of the network devices 14, 16 comprises a computer system including a processor 40, memory 42 including software 44, transmitter(s) 46, antenna(s) 48, receiver(s) 50, and a network interface 52. The transmitters 46, antennas 48, and receivers 50 form a wireless communication module that can communicate with the MS 12 and mobile devices (e.g., mobile phones, tablet computers, personal digital assistants, etc.) and/or another entity. The transmitters 46 and receivers 40 are configured to communicate bi-directionally with the MS 12 and one or more mobile devices via the antennas 28. The transmitters 46 and receivers 40 are configured to communicate bi-directionally (wirelessly through an antenna 48 or with other devices not shown such as a server. The processor 40 is preferably an intelligent hardware device, e.g., a central processing unit (CPU) such as those made by ARM®, Intel® Corporation, or AMD®, a microcontroller, an application specific integrated circuit (ASIC), etc. The processor 40 could comprise multiple separate physical entities that can be distributed in the AP 14. The memory 42 includes random access memory (RAM) and read-only memory (ROM). The memory 42 is a processor-readable storage medium that stores the software 44 which is processor-readable, processor-executable software code containing processor-readable instructions that are configured to, when executed, cause the processor 40 to perform various functions described herein. Alternatively, the software 44 may not be directly executable by the processor 40 but configured to cause the processor 40, e.g., when compiled and executed, to perform the functions. The network interface 52 is configured to communicate bi-directionally with the network 19 (FIG. 2).

Referring to FIG. 5, the server 19 comprises a computer system including a processor 60, memory 62 including software 64, and a network interface 66. The processor 60 is preferably an intelligent hardware device, e.g., a central processing unit (CPU) such as those made by ARM®, Intel® Corporation, or AMD®, a microcontroller, an application specific integrated circuit (ASIC), etc. The processor 60 could comprise multiple separate physical entities that can be distributed in the server 19. The memory 62 includes random access memory (RAM) and read-only memory (ROM). The memory 62 is a processor-readable storage medium that stores the software 64 which is processor-readable, processor-executable software code containing processor-readable instructions that are configured to, when executed, cause the processor 60 to perform various functions described herein (although the description may refer only to the processor 60 performing the functions). Alternatively, the software 64 may not be directly executable by the processor 60 but configured to cause the processor 60, e.g., when compiled and executed, to perform the functions. The network interface 66 is configured to communicate bi-directionally with the network 18 (FIG. 2) to send communications to and receive communications from the BTS 16 and/or the APs 14 through the network 18.

Referring to FIG. 6, network devices, here the APs 14 ₁, 14 ₂ shown in FIG. 2, each include the components shown. Each of the APs 14 ₁, 14 ₂, respectively, includes functional elements of a measurement module 80 ₁, 80 ₂, an observer module 82 ₁, 82 ₂, a MAC 84 ₁, 84 ₂, and includes a transceiver 86 ₁, 86 ₂ that each comprises the transmitters 46, the antennas 48, and the receivers 50 shown in FIG. 4. The modules 80, 82 are each implemented, e.g., by the processor 40 and the memory 42, including the software 44. The measurement modules 80 are configured to obtain (e.g., access or prepare) a message and send the message via the transceivers 86 toward the MS 12 and to receive via the transceivers 86 the acknowledgement from the MS 12. The measurement modules 80 are further configured to send indications of the transmit time of the message from the MACs 84 and the receipt time of the acknowledgement at the MACs 84 toward the server 19. The modules 80, 82 of each of the APs 14 ₁, 14 ₂ are further configured to work with the module 80, 82 of other network devices, e.g., other APs 14, to determine a transmit time from a message leaving the MAC 84 of one AP 14 to arriving at the MAC 84 of the other AP 14. The observer modules 82 are configured to receive via the transceivers 86 the acknowledgement from the MS 12 and to send an indication of the receipt time of the acknowledgement at the MAC 84 toward the server 19. These functions are discussed further below with respect to FIG. 8.

Observer-Based Time-of-Arrival

The following provides a discussion of observer-based time-of-arrival (TOA) determination to find an accurate position (location) for a target device, that is a network device with an unknown position, using multiple network devices with known positions. Measurements can be performed using one or more observer APs 14 to reduce or even eliminate dependence on variable SIFS ACK signal turnaround time. The discussion below focuses on determining a position of the mobile device 12. The techniques discussed, however, may be applied to determine a position of another device, e.g., any network device such as any of the network devices 12, 14, 16 shown in FIG. 2. Techniques discussed are directed to determining a position of a target device with an unknown position by taking measurements using at least two devices with known positions, and processing results of these measurements to determine the position of a target device. In particular, techniques are discussed for determining a position of a network device with an unknown position, and that is in a responding mode, using network devices with known positions. The discussions, however, are examples and not limiting of the scope of the disclosure.

Referring to FIG. 7, the server 19 includes a control engine (controlling means or control means) 90, and a position engine (positioning means or position determining means) 92. The engines 90, 92 are functional modules implemented by the processor 60 and the software 64 stored in the memory 62. Thus, reference to the engines 90, 92 performing or being configured to perform a function is shorthand for the processor 60 performing or being configured to perform the function in accordance with the software 64 (and/or firmware, and/or hardware of the processor 60). Similarly, reference to the processor 60 performing a controlling or position determination function is equivalent to the control engine 90 or the position engine 92, respectively, performing the function. The control engine 90 is communicatively coupled to the position engine 92, e.g., to share information to be used to determine the target device's position (e.g., which network device(s) is(are) a measurement network device(s) and which network device(s) is(are) an observer network device(s)). The control engine 90 is communicatively coupled to the network interface 66 for instructing (e.g., for sending control instructions to instruct) the network devices and for receiving indications of status of the network devices (e.g., measurements complete). The position engine 92 is communicatively coupled to the network interface 66 for receiving timing information and other information (e.g., positions of known-position devices) from the network devices, and sending position indications of positions of target devices.

The control engine 90 is configured to control the access points 14 to obtain and report observer-based time-of-arrival information. The control engine 90 is configured to select network devices, 12, 14, 16, e.g., access points 14, as measurement-observer combinations (e.g., pairs), and to send signals/commands to the selected network devices 12, 14, 16 to indicate to the selected network devices 12, 14, 16 that the selected network devices 12, 14, 16 have been selected as a measurement-observer combination or measurement-observer combinations. The control engine 90 is also configured to cause the selected measurement-observer combination(s) to initiate measurements, and to provide parameter information about the measurements, e.g., an amount of time to be used for measurements. In particular, the network devices 12, 14, 16 are configured to change from a home channel to a measurement channel, send measurement signals for use in RTT and TOA determinations, track times of transmission and arrival of the test signals, and report the times of transmission and arrival (timing information) to the server 19, in particular to the position engine 92, as measurement information.

The position engine 92 is configured to determine a position of a target device, e.g., the mobile device 12, based on the reported measurement information from the measurement-observer combination(s) and other appropriate information. The position engine 92 is configured to obtain, e.g., receive and collect, measurement information obtained during measurements by the measurement-observer combination(s) of the selected network devices 12, 14, 16. The position engine 92 is further configured to use the measurement information to determine a position (location) of the target device.

Referring to FIG. 8, with further reference to FIGS. 2-7, a process 110 of determining the position of the mobile device 12 using observer-based TOA information includes the stages shown. The process 110 is, however, an example only and not limiting. The process 110 can be altered, e.g., by having stages added, removed, rearranged, combined, performed concurrently, and/or having single stages split into multiple stages. The process 110 discusses an example of determining the position of the mobile device 12 as the target device using the APs 14 ₁, 14 ₂ as a measurement-observer combination, here a measurement-observer pair. The process 110, however, may be used for different combinations of network devices, i.e., other than with the mobile device 12 as the target device and/or other than with the APs 14 ₁, 14 ₂ used as a measurement-observer combination.

At stage 112, the process 110 includes sending a first measurement signal from a first known-position device. For example, the first known-position device may be a measurement access point such as the AP 14 ₁, having a first known position. In this example, the measurement AP 14 ₁, in particular the measurement module 80 ₁, wirelessly broadcasts a measurement signal (MS) that can be received by an observer device and the target device, in this example the observer AP 14 ₂ (having a second known position) and the mobile device 12, respectively.

At stage 114, the process 110 includes receiving the first measurement signal at a second known-position device. Continuing the example, the observer AP 14 ₂ wirelessly receives the measurement signal MS from the measurement AP 14 ₁.

At stage 116, the process 110 includes receiving a first acknowledgement signal from the target device at the first known-position device and at the second known-position device. Continuing the example, the mobile device 12 is in a responding mode and wirelessly sends an acknowledgement signal (ACK) in response to receiving the measurement signal MS. Stage 116 includes the measurement AP 14 ₁ and the observer AP 14 ₂ wirelessly receiving this acknowledgement signal ACK.

At stage 118, the process 110 includes determining the position of the target device using first timing information associated with the first measurement signal and the first acknowledgement signal, a first position of the first known-position device, and a second position of the second known-position device. Continuing the example, the measurement AP 14 ₁ and the observer AP 14 ₂ send timing information regarding receipt times of the measurement signal MS and the acknowledgement signal ACK to the server (FIG. 2). The server 19, in particular the position engine 92, uses the timing information to determine the position of the mobile device 12.

Referring to FIG. 9, with further reference to FIGS. 2-7, a process 130 of determining the position of a target device using observer-based TOA information includes the stages shown. The process 130 is, however, an example only and not limiting. The process 130 can be altered, e.g., by having stages added, removed, rearranged, combined, performed concurrently, and/or having single stages split into multiple stages. For example, stage 138 could be split into two stages, with measurement information with access points in first roles reported before stage 136, where the roles are changed. Further, stage 136 could be eliminated. Still other alterations to the process 130 as shown and described are possible. The process 130 discusses an example of determining the position of the mobile device 12 as the target device using the APs 14 ₁, 14 ₂ as a measurement-observer combination, here a measurement-observer pair. The process 130, however, may be used for different combinations of network devices, i.e., other than with the mobile device 12 as the target device and/or other than with the APs 14 ₁, 14 ₂ used as a measurement-observer combination.

At stage 132, the server 19 selects measurement-observer pairs of the access points 14. For example, the control engine 90 sends instructions to the access points 14 ₁, 14 ₂ to be a measurement-observer pair, e.g., to cause the access point 14 ₁ to be a measurement network device (here a measurement AP) and to cause the access point 14 ₂ to be an observer network device (here an observer AP). The control engine 90 thus instructs the access point 14 ₁ to act as a measurement network device and the access point 14 ₂ to act as an observer network device concurrently. That is, the access point 14 ₁ will act as a measurement network device currently with the access point 14 ₂ acting as an observer network device based on instruction from the control engine 90. The control engine 90 sends instructions to other pairs of the access points 14 to be separate measurement-observer pairs separate from the access points 14 ₁, 14 ₂. For example, the control engine 90 may send signals to eight of the access points 14 to form four separate measurement-observer pairs, although other quantities of measurement-observer pairs may be used. Further, the control engine 90 may limit the quantity of access points 14 performing timing measurements at a given time in a given area, e.g., to four (two measurement-observer pairs). The remaining discussion of the process 130 focuses on one measurement-observer pair containing the access points 14 ₁, 14 ₂, but the discussion applies to other access points 14 as well.

At stage 134, the access points 14 ₁, 14 ₂ perform time measurements. The access points 14 ₁, 14 ₂ respond to the instructions from the server 19 by setting their respective currently-used communication channels to a common (i.e., the same) measurement channel (e.g., changing from a home channel as appropriate) and performing measurements. At first, the access point 14 ₁ is the measurement AP and the access point 14 ₂ is the observer AP. The access points 14 ₁, 14 ₂ perform a TSF (time synchronization function) sync to a primary connected access point of the access points 14 ₁, 14 ₂ , targeting the primary connected access point's next beacon time. The access point 14 ₁ starts measurement frames exchange at the next beacon time and the access point 14 ₂ observes. Here, the access point 14 ₁ sends a measurement signal that is received by the mobile device 12 and the access point 14 ₂. The mobile device 12 responds to receiving the measurement signal by sending an acknowledgement signal. The acknowledgement signal is received by the access points 14 ₁, 14 ₂. The access points 14 ₁, 14 ₂ determine the time of transmission of the measurement signal and the times of receipt of the measurement signal and the acknowledgement signal. These times may be stored, at least temporarily (e.g., as part of shift registers or in the memory 42), for transmission to the server 19.

At stage 136, the roles of the access points 14 ₁, 14 ₂ change. The measurement AP sends a measurement-complete indication or exchange message to the observer AP when the measurements by the measurement AP are done. The measurement AP responds to the sending of this indication or message by becoming the observer AP and the observer AP responds to receiving this indication or message by becoming the measurement AP and thereafter acting as the measurement AP including sending an MS. The transmission time measurements of stage 134 are repeated with the access points 14 ₁, 14 ₂ in their new roles. The access points 14 ₁, 14 ₂ attempt to complete their measurements (as measurement AP and observer AP combined) in a designated interval, e.g., a 32 ms interval. If the measurements are not completed within the designated time period, the present measurement AP, here the access point 14 ₂, coordinates with the observer AP to continue measurements within the same beacon interval. This stage may be omitted, but may improve efficiency by increasing measurements obtained for a single change in channels to the measurement channel by the access points 14 ₁, 14 ₂.

At stage 138, the measurement information collected by the access points 14 ₁, 14 ₂ during the transmission time measurements is reported. The access points 14 ₁, 14 ₂ collect information about the measurements and report the collected information to the position engine 92 of the server 19. Timing information from the transmission time measurements may be reported at one or more times, e.g., when the information is obtained, at the transition between roles of the access points 14 ₁, 14 ₂, or after all timing measurements are completed, etc. Each of the access points 14 ₁, 14 ₂ changes its currently-used communication channel to a communication channel other than the measurement channel, e.g., to their respective home channels. The currently-used communication channels of the access points 14 ₁, 14 ₂ may or may not be the same channel. If there are more measurement-observer pairs of access points 14 that have not yet obtained and reported measurement information, then those access points 14 change their currently-used communication channels the measurement channel and the process 130 returns to stage 134.

At stage 140, the server 19 determines the position of the mobile device 12 based on the reported measurement information. The position engine 92 uses the reported timing information from one or more, preferably all, of the measurement- observer pairs, in combination with locations of the access points 14 to determine the location of the mobile device 12. If a desired accuracy of position of the mobile device 12 is not achieved (e.g., a horizontal estimated position error (HEPE) being undesirable (e.g., exceeding a threshold)), then the process 130 will return to stage 132 and the control engine 90 will select a different set of access points 14 to use as measurement-observer pairs, although some of the newly selected access points 14 may have been used previously in a measurement-observer pair. Alternatively, the position determination could be made at an entity other than the server 19 in the system 10, with the other entity obtaining the timing information and having or obtaining other relevant information for determining the position of the mobile device 12.

Referring to FIG. 10, with further reference to FIGS. 2-7 and 11, a process 150 of determining the position of a target device, here the mobile device 12, using observer-based TOA information includes the stages shown. The process 150 is, however, an example only and not limiting. The process 150 can be altered, e.g., by having stages added, removed, rearranged, combined, performed concurrently, and/or having single stages split into multiple stages. The process 150 discusses an example of determining the position of the mobile device 12 as the target device using the APs 14 ₁, 14 ₂ as a measurement-observer combination, here a measurement-observer pair with known positions (i.e., a measurement-observer known-position device pair). The process 150, however, may be used for different combinations of network devices, i.e., other than with the mobile device 12 as the target device and/or other than with the APs 14 ₁, 14 ₂ used as a measurement-observer combination. The discussion below regarding the process 150 focuses on the access points 14 ₁, 14 ₂, e.g., after being selected as a measurement-observer pair (see stage 132 of FIG. 9), but the discussion applies to other access points 14 as well. For simplicity in subscripts, the measurement AP shown in FIG. 11 is designated as a measurement AP (1), the observer AP is designated as an observer AP (3), and the mobile device 12 is designated as a mobile device (2). The outer ovals for the access points 14 ₁, 14 ₂, represent timing of signals leaving from or reaching one or more of the antennas 48, the outer oval for the mobile device 12 represents timing of signals leaving from or reaching one or more of the antennas 28, and the inner ovals of the access points 14 ₁, 14 ₂, and the mobile device 12 represent timing of signals leaving from or reaching the MACs 84, 85, respectively.

At stage 152, the access points 14 ₁, initially being the measurement AP, sends a measurement signal (MS) toward the mobile device 12 and the access points 14 ₂. Having been selected, the access points 14 ₁, 14 ₂, change to the same measurement channel and the access point 14 ₁ broadcasts the MS so that the MS can be received by the mobile device 12 and the observer AP, initially the access points 14 ₂. The MS is initiated in the MAC 84 ₁ and sent through the transceiver 86 ₁ including through the antenna 88 ₁. The amount of time for the MS to transfer (i.e., the transfer time) from the MAC 84 ₁ out the antenna 88 ₁ is represented in FIG. 11 as TX₁. The time (i.e., the moment in time) that the MS leaves the MAC 84 ₁ is the time of transmission and is represented in FIG. 11 as T₀. The measurement AP (here the access point 14 ₁) stores the time T₀ (i.e., the time of transmission of the MS from the MAC 84 of the measurement AP) in its memory 42.

At stage 154, the access point 14 ₂, initially being the observer AP, receives the MS. The access point 14 ₂ receives the MS through the transceiver 86 ₂, including the antenna 88 ₂, and into the MAC 84 ₂. The amount of time for the MS to transfer from the antenna 88 ₁ of the access point 14 ₁ to the antenna 88 ₂ of the access point 14 ₂ is represented in FIG. 11 as t₃₁. The amount of time for the MS to transfer from the antenna 88 ₂ to the MAC 84 ₂ is represented in FIG. 11 as RX′₃₁. The time of arrival (TOA) of the MS (i.e., the moment in time that the MS arrives) at the MAC 84 ₂ is represented in FIG. 11 as T₂. The observer AP (here the access point 14 ₂) stores the time T₂ in its memory 42.

At stage 154, the mobile device 12 receives the MS. The mobile device 12 receives the same MS that the observer AP received. The mobile device 12 receives the MS through the antenna 28 and the receiver 30 and into a MAC 85. The amount of time for the MS to transfer from the antenna 88 ₁ of the access point 14 ₁ to the antenna 28 of the mobile device 12 is represented in FIG. 11 as t₂₁. The amount of time for the MS to transfer from the antenna 28 to the MAC 85 is represented in FIG. 11 as RX′₂₁.

At stage 158, the mobile device 12 sends an acknowledgement (ACK) signal. The mobile device 12 responds to receiving the MS signal by broadcasting the ACK signal so that the ACK signal can be received by the measurement AP (initially the access point 14 ₁) and the observer AP (initially the access point 14 ₂).

At stage 160, the ACK signal is received at the measurement AP and at the observer AP. The access point 14 ₂ (at this time, the observer AP) receives the ACK signal through the transceiver 86 ₂, including the antenna 88 ₂, and into the MAC 84 ₂. The amount of time for the ACK signal to transfer from the antenna 28 of the mobile device 12 to the antenna 88 ₂ of the access point 14 ₂ is represented in FIG. 11 as t₃₂. The amount of time for the ACK signal to transfer from the antenna 88 ₂ to the MAC 84 ₂ is represented in FIG. 11 as RX′₃₂. The TOA of the ACK signal at the MAC 84 ₂ is represented in FIG. 11 as T₃. The access point 14 ₂ (here the observer AP) stores the time T₃ in its memory 42. The access point 14 ₁ (at this time, the measurement AP) receives the ACK signal through the transceiver 86 ₁, including the antenna 88 ₁, and into the MAC 84 ₁. The transmission time, i.e., the amount of time for the ACK signal to transfer from the antenna 28 of the mobile device 12 to the antenna 88 ₁ of the access point 14 ₁, is represented in FIG. 11 as t₁₂ (where the transmission time t₁₂ equals the amount of time t₂₁). The amount of time for the ACK signal to transfer from the antenna 88 ₁ to the MAC 84 ₁ is represented in FIG. 11 as RX′₁₂. The TOA of the ACK signal at the MAC 84 ₁ is represented in FIG. 11 as T₁. The access point 14 ₁ (here the measurement AP) stores the time T₁ in its memory 42.

At stage 162, the times of arrival of the MS and the ACK signal, and the time of transmission of the MS, are reported to the server 19. The access points 14 ₁, 14 ₂, respectively, send the time of transmission T₀ of the MS and the arrival time T₁ of the ACK signal, and the arrival time T₂ of the MS and the arrival time T₃ of the ACK signal at the respective MACs 84 to the position engine 92 of the server 19. As discussed above, these times may be reported at various times, e.g., before the access points 14 ₁, 14 ₂ change measurement and observer roles, or after changing roles (i.e., the access point 14 ₁ changing to the observer AP and the access point 14 ₂ changing to the measurement AP), as soon as the times are measured or otherwise determined, after all measurements are completed for the measurement-observer pair, etc.

At stage 164, the server 19 determines the mobile device position based on the reported measurement information. The position engine 92 uses the reported transmission and arrival times to determine the transfer times between the mobile device 12 and the access points 14 ₁, 14 ₂. The position engine 92 will use these times, the known locations of the access points 14 ₁, 14 ₂, and other appropriate information (e.g., the speed of light) to determine distances (which may be estimated distances) from the access points 14 ₁, 14 ₂ to the mobile device 12, and thus the position of the mobile device 12 using trilateration. The process 150 can be performed for one or more further measurement-observer known-position device pairs to obtain further timing information and to use the further timing information, alone or in combination with the timing information obtained from the measurement-observer pair of the access points 14 ₁, ¹⁴ ₂, to determine the position of the mobile device 12, e.g., using trilateration.

The position engine 92 is configured to determine a difference in the transfer times between the mobile device 12 and the access points 14 ₁, 14 ₂. To do this, the position engine is configured to determine a difference between (1) a difference between the arrival time T₁ of the ACK signal at the measurement AP and the time of transmission T₀ of the MS by the measurement AP and (2) a difference between the arrival time T₃ of the ACK signal at the observer AP and the arrival time T₂ of the ACK signal at the observer AP. The difference between the arrival time T₁ of the ACK signal at the measurement AP and the time of transmission T₀ of the MS by the measurement AP is given by:

T ₁ −T ₀ =TX ₁ +t ₂₁ +RX′ ₂₁ +SIFS+TX ₂ +t ₁₂ +RX′ ₁₂   (2)

where SIFS (short inter-frame space) is a turnaround time of the MAC 85 of the mobile device 12 from receipt of the MS at the MAC 85 to transmission of the ACK signal from the MAC 85. The difference between the arrival time T₃ of the ACK signal at the observer AP and the arrival time T₂ of the ACK signal at the observer AP is given by:

T ₃ −T ₂ =t ₂₁ +RX′ ₂₁ +SIFS+TX ₂ +t ₃₂ +RX′ ₃₂−(t ₃₁ +RX′ ₃₁)   (3)

Taking the difference between Eqn. (1) and Eqn. (2) yields:

(T ₁ −T ₀)−(T ₃ −T ₂)=t₁₂ −t ₃₂ +RX′ ₁₂ +RX′ ₃₂ +t ₃₁ +TX ₁ +RX′ ₃₁   (4)

where the expression t₃₁+TX₁+RX′₃₁ is a determinable constant and the terms RX′₁₂ and RX′₃₂ are known values for the measurement AP and the observer AP, respectively. The value of the expression t₃₁+TX₁+RX′₃₁ is the transmission time from the MAC 84 of the measurement AP to the MAC 84 of the observer AP and can be determined by determining a difference of the arrival time T₂ of the MS at the MAC 84 of the observer AP and the time of transmission T₀ of the MS from the MAC 84 of the measurement AP. This value may be determined in the background between the measurement and observer APs, i.e., separate from the process 150, e.g., by sending a test signal and determining the travel time from the MAC of the measurement AP to the MAC of the observer AP. The values of the terms RX′₁₂ and RX′₃₂ can be determined during manufacture of the access points 14 and stored in their respective memories 22, predetermined values for these terms can be stored in the memories 22 of all the access points 14 in the system 10 without individual determination, the predetermined values can be stored in the memory 62, etc. Further, the values for the terms RX′₁₂ and RX′₃₂ may be assumed to be the same, e.g., where the values are not individually determined

By evaluating Eqn. (4) with the known/determinable values discussed above, the position engine 92 can determine a value of the difference, t₁₂−t₃₂, in the transfer times between the mobile device 12 and the access points 14 ₁, 14 ₂. The position engine 92 is configured to determine the set of locations where this difference equals the determined value, which constitute possible locations for the mobile device 12. The position engine 92 can determine similar sets of locations with the measurement/observer roles of the access points 14 ₁, 14 ₂ reversed, as well as similar sets of locations for other measurement-observer pairs of access points 14. The position engine 92 is configured to determine the location of the mobile device 12 as the point that best satisfies the various sets of possible, estimated locations, determined from using the measurement-observer pairs.

While the discussions above with respect to FIGS. 8-11 discussed examples with measurement-observer combinations of measurement-observer pairs, other combinations of devices may be used. For example, combinations with a target device, a measurement device, and multiple observer devices associated with the measurement device may be used, with the measurement device and the observer devices having known positions. Referring to FIG. 12, a combination 200 of devices includes a target device 202, a measurement device 204, and three observer devices 206, 208, 210. In cases with multiple observer devices for a single measurement device, the measurement signal MS sent by the measurement device is received by the multiple observer devices and the multiple observer devices provide their respective timing information to the server 19 and the position engine 92 determines position estimates of the target device using the information from the multiple observer devices. FIG. 12 shows only one measurement device, but there may be one or more other measurement devices associated with at least one observer device each. Any of these observer devices may be one of the observer devices 206, 208, 210, with the observer devices able to identify the source of the measurement signal MS and report this to the position engine 92 along with the corresponding timing information. Also in this case, the observer devices operate concurrently even though the measurement signal MS may arrive at the observer devices at different times and/or the acknowledgement signal ACK may arrive at the observer devices at different times and/or the observer devices may send their respective timing information at different times to the server 19. The devices initially serving as the multiple observer devices may be selected to send a measurement signal MS. For example, the control engine 90 may have one of these devices (e.g., the device 206) switch roles with the measurement device (e.g., the device 204), or may have more than one of these devices become measurement devices to set up different measurement-observer combinations (e.g., the devices 204 and 206 becoming measurement devices with the device 208 being paired as an observer device with the device 204 and the device 210 being paired as an observer device with the device 206). If a sufficient quantity (e.g., three or more) observer devices are used, then a position of the target device may be determined with desired accuracy (e.g., a HEPE within a desired threshold) without having to perform a further measurement (e.g., another device serving as a measurement device, be it one of the devices initially serving as one of the multiple observer devices, or another device).

Referring to FIG. 13, with further reference to FIGS. 2-7 and 11, a method 230 of determining the position of a target device, here the mobile device 12, using observer-based TOA information includes the stages shown. The process 230 is, however, an example only and not limiting. The process 230 can be altered, e.g., by having stages added, removed, rearranged, combined, performed concurrently, and/or having single stages split into multiple stages.

At stage 232, the method 230 includes sending a first instruction to a first network device to act as a measurement network device to send a first measurement signal. The control engine 90 of the server 19 can send a command signal to instruct a network device, e.g., the access point 14 ₁, to be a measurement device and, as such, to send a measurement signal.

At stage 234, the method 230 includes sending a second instruction to a second network device to act as an observer network device to receive the first measurement signal, the first network device having a first known position and the second network device having a second known position. The control engine 90 sends a command signal to a network device, e.g, the access point 14 ₂, to be an observer device. The access points 14 ₁, 14 ₂, have known positions.

At stage 236, the method 230 includes receiving first timing information associated with the first measurement signal. The access points 14 ₁, 14 ₂ send timing information associated with the measurement signal, e.g., time of transmission of the measurement signal, time of receipt of the measurement signal, and/or time or receipt of an acknowledgement signal sent by the mobile device 12 in response to receiving the measurement signal.

At stage 238, the method 230 includes determining the position of the target device based on the first timing information, the first known position, and the second known position. The position engine 92 collects the timing information and uses this in combination with the known positions of the access points 14 ₁, 14 ₂ to determine the position of the mobile device 12, e.g., by determining distances from the 14 ₁, 14 ₂ and using trilateration.

Further, while the discussion above focused on examples where the measurement device(s) sends a single measurement signal MS, other implementations may be used. For example, a measurement device may send multiple measurement signals. How many measurement signals the measurement device sends may vary, e.g., depending on a threshold amount of time, a threshold number of measurement signals, until the control engine 90 sends a command to stop sending the measurement signals (e.g., in response to the position engine 92 receiving timing information from a desired quantity (e.g., all) of the observer devices associated with the measurement device, etc.).

The measurement signal MS may take a variety of forms. For example, the measurement signal may be a single packet of information or multiple packets of information.

Further Considerations

As used herein, including in the claims, “or” as used in a list of items prefaced by “at least one of” indicates a disjunctive list such that, for example, a list of “at least one of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., A and B and C), or combinations with more than one feature (e.g., AA, AAB, ABBC, etc.).

As used herein, including in the claims, unless otherwise stated, a statement that a function or operation is “based on” an item or condition means that the function or operation is based on the stated item or condition and may be based on one or more items and/or conditions in addition to the stated item or condition.

A wireless communication network does not have all communications transmitted wirelessly, but is configured to have at least some communications transmitted wirelessly.

Other examples and implementations are within the scope and spirit of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations.

Further, more than one invention may be disclosed.

Substantial variations to described configurations may be made in accordance with specific requirements. For example, customized hardware might also be used, and/or particular elements might be implemented in hardware, software (including portable software, such as applets, etc.), or both. Further, connection to other computing devices such as network input/output devices may be employed.

Common forms of physical and/or tangible computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read instructions and/or code.

The methods, systems, and devices discussed above are examples. Various configurations may omit, substitute, or add various procedures or components as appropriate. For instance, in alternative configurations, the methods may be performed in an order different from that described, and that various steps may be added, omitted, or combined. Also, features described with respect to certain configurations may be combined in various other configurations. Different aspects and elements of the configurations may be combined in a similar manner. Also, technology evolves and, thus, many of the elements are examples and do not limit the scope of the disclosure or claims.

Specific details are given in the description to provide a thorough understanding of example configurations (including implementations). However, configurations may be practiced without these specific details. For example, well-known circuits, processes, algorithms, structures, and techniques have been shown without unnecessary detail in order to avoid obscuring the configurations. This description provides example configurations only, and does not limit the scope, applicability, or configurations of the claims. Rather, the preceding description of the configurations provides a description for implementing described techniques. Various changes may be made in the function and arrangement of elements without departing from the spirit or scope of the disclosure.

Also, configurations may be described as a process which is depicted as a flow diagram or block diagram. Although each may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be rearranged. A process may have additional stages or functions not included in the figure. Furthermore, examples of the methods may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware, or microcode, the program code or code segments to perform the tasks may be stored in a non-transitory computer-readable medium such as a storage medium. Processors may perform the described tasks.

Having described several example configurations, various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosure. For example, the above elements may be components of a larger system, wherein other rules may take precedence over or otherwise modify the application of the invention. Also, a number of operations may be undertaken before, during, or after the above elements are considered. Accordingly, the above description does not bound the scope of the claims.

A statement that a value exceeds (or is more than) a first threshold value is equivalent to a statement that the value meets or exceeds a second threshold value that is slightly greater than the first threshold value, e.g., the second threshold value being one value higher than the first threshold value in the resolution of a computing system. A statement that a value is less than (or is within) a first threshold value is equivalent to a statement that the value is less than or equal to a second threshold value that is slightly lower than the first threshold value, e.g., the second threshold value being one value lower than the first threshold value in the resolution of a computing system. 

What is claimed is:
 1. A method of determining a position of a target device, the method comprising: sending a first measurement signal from a first known-position device; receiving the first measurement signal at a second known-position device; receiving a first acknowledgement signal from the target device at the first known-position device and at the second known-position device; and determining the position of the target device using first timing information associated with the first measurement signal and the first acknowledgement signal, a first position of the first known-position device, and a second position of the second known-position device.
 2. The method of claim 1 wherein the first timing information comprises a transmission time of the first measurement signal, a first time of arrival of the first acknowledgement signal in the first known-position device, a second time of arrival of the first measurement signal in the second known-position device, and a third time of arrival of the first acknowledgement signal in the second known-position device, and wherein using the first timing information comprises determining a first distance and a second distance from the target device to the first known-position device and the second known-position device, respectively, using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival.
 3. The method of claim 2 wherein using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival comprises determining a difference between (1) a difference between the first time of arrival and the transmission time and (2) a difference between the third time of arrival and the second time of arrival.
 4. The method of claim 1 further comprising: receiving the first measurement signal at a third known-position device; and receiving the first acknowledgement signal from the target device at the third known-position device; wherein the first timing information comprises a transmission time of the first measurement signal, a first time of arrival of the first acknowledgement signal in the first known-position device, a fourth time of arrival of the first measurement signal in the third known-position device, and a fifth time of arrival of the first acknowledgement signal in the third known-position device; and wherein using the first timing information comprises determining a third distance from the target device to the third known-position device using the fourth time of arrival and the fifth time of arrival.
 5. The method of claim 1 further comprising: sending a second measurement signal from the second known-position device; receiving the second measurement signal at the first known-position device; and receiving a second acknowledgement signal from the target device at the first known-position device and at the second known-position device; wherein determining the position of the target device further comprises using second timing information associated with the second measurement signal and the second acknowledgement signal.
 6. The method of claim 5 further comprising sending an exchange message from the first known-position device indicating receipt of the first acknowledgement signal, wherein the second measurement signal is sent from the second known-position device in response to the exchange message being received by the second known-position device.
 7. The method of claim 5 wherein the first known-position device and the second known-position device form a measurement-observer known-position device pair, the method further comprising obtaining further timing information from a plurality of further measurement-observer known-position device pairs for the target device, and wherein determining the position of the target device further comprises using the further timing information to determine the position of the target device using trilateration.
 8. An apparatus for determining a position of a target device, the apparatus comprising: a network interface; a control engine communicatively coupled to the network interface and configured to: send, via the network interface, a first instruction to a first network device to act as a measurement network device to send a first measurement signal; and send, via the network interface, a second instruction to a second network device to act as an observer network device to receive the first measurement signal, the first network device having a first known position and the second network device having a second known position; and a position engine, communicatively coupled to the control engine and the network interface, configured to: receive, via the network interface, first timing information associated with the first measurement signal; and determine the position of the target device based on the first timing information, the first known position, and the second known position.
 9. The apparatus of claim 8 wherein: the first timing information comprises: a transmission time of the first measurement signal; a first time of arrival in the first network device of a first acknowledgement signal sent by the target device in response to receiving the first measurement signal; a second time of arrival of the first measurement signal in the second network device; and a third time of arrival of the first acknowledgement signal in the second network device; and the position engine, to determine the position of the target device, is configured to determine a first distance and a second distance from the target device to the first network device and the second network device, respectively, using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival.
 10. The apparatus of claim 9 wherein using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival comprises determining a difference between (1) a difference between the first time of arrival and the transmission time and (2) a difference between the third time of arrival and the second time of arrival.
 11. The apparatus of claim 8 wherein: the control engine is further configured to instruct a third network device to act as another observer network device, the third network device having a third known position; the first timing information further comprises: a fourth time of arrival of the first measurement signal in the third network device; and a fifth time of arrival of a first acknowledgement signal in the third network device; and the position engine, to determine the position of the target device, is further configured to determine a third distance from the target device to the third network device using the fourth time of arrival and the fifth time of arrival.
 12. The apparatus of claim 8 wherein: the control engine is further configured to instruct the first network device to act as the observer network device and the second network device to act as the measurement network device; and the position engine is further configured to: receive, via the network interface, second timing information associated with a second measurement signal sent from the second network device and received by the first network device while acting as the observer network device; and determine the position of the target device further based on the second timing information.
 13. An apparatus for determining a position of a target device, the apparatus comprising: a network interface; control means, communicatively coupled to the network interface, for: sending, via the network interface, a first instruction to a first network device to act as a measurement network device to send a first measurement signal; and sending, via the network interface, a second instruction to a second network device to act as an observer network device to receive the first measurement signal, the first network device having a first known position and the second network device having a second known position; and position determining means, communicatively coupled to the control means and the network interface, for: receiving, via the network interface, first timing information associated with the first measurement signal; and determining the position of the target device based on the first timing information, the first known position, and the second known position.
 14. The apparatus of claim 13 wherein: the first timing information comprises: a transmission time of the first measurement signal; a first time of arrival in the first network device of a first acknowledgement signal sent by the target device in response to receiving the first measurement signal; a second time of arrival of the first measurement signal in the second network device; and a third time of arrival of the first acknowledgement signal in the second network device; and the position determining means, for determining the position of the target device, is configured to determine a first distance and a second distance from the target device to the first network device and the second network device, respectively, using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival.
 15. The apparatus of claim 14 wherein using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival comprises determining a difference between (1) a difference between the first time of arrival and the transmission time and (2) a difference between the third time of arrival and the second time of arrival.
 16. The apparatus of claim 13 wherein: the control means is further for instructing a third network device to act as another observer network device, the third network device having a third known position; the first timing information further comprises: a fourth time of arrival of the first measurement signal in the third network device; and a fifth time of arrival of a first acknowledgement signal in the third network device; and the position determining means, for determining the position of the target device, is further configured to determine a third distance from the target device to the third network device using the fourth time of arrival and the fifth time of arrival.
 17. The apparatus of claim 13 wherein: the control means is further configured to instruct the first network device to act as the observer network device and the second network device to act as the measurement network device; and the position determining means is further for: receiving, via the network interface, second timing information associated with a second measurement signal sent from the second network device and received by the first network device while acting as the observer network device; and determining the position of the target device further based on the second timing information.
 18. A processor-readable storage medium comprising processor-readable instructions configured to cause a processor to: send a first instruction to a first network device to act as a measurement network device to send a first measurement signal; send a second instruction to a second network device to act as an observer network device to receive the first measurement signal, the first network device having a first known position and the second network device having a second known position; receive first timing information associated with the first measurement signal; and determine a position of a target device based on the first timing information, the first known position, and the second known position; wherein the first timing information is associated with the first measurement signal.
 19. The processor-readable storage medium of claim 18 wherein: the first timing information comprises: a transmission time of the first measurement signal; a first time of arrival in the first network device of a first acknowledgement signal sent by the target device in response to receiving the first measurement signal; a second time of arrival of the first measurement signal in the second network device; and a third time of arrival of the first acknowledgement signal in the second network device; and the instructions configured to cause the processor to determine the position of the target device are configured to cause the processor to determine a first distance and a second distance from the target device to the first network device and the second network device, respectively, using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival.
 20. The processor-readable storage medium of claim 19 wherein using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival comprises determining a difference between (1) a difference between the first time of arrival and the transmission time and (2) a difference between the third time of arrival and the second time of arrival.
 21. The processor-readable storage medium of claim 18 wherein: the instructions further comprise instructions configured to cause the processor to instruct a third network device to act as another observer network device, the third network device having a third known position; the first timing information further comprises: a fourth time of arrival of the first measurement signal in the third network device; and a fifth time of arrival of a first acknowledgement signal in the third network device; and the instructions configured to cause the processor to determine the position of the target device are configured to cause the processor to determine a third distance from the target device to the third network device using the fourth time of arrival and the fifth time of arrival.
 22. The processor-readable storage medium of claim 18 further comprising instructions configured to cause the processor to instruct the first network device to act as the observer network device and the second network device to act as the measurement network device, wherein the instructions configured to cause the processor to determine the position of the target device are configured to cause the processor to: receive, via the network interface, second timing information associated with a second measurement signal sent from the second network device and received by the first network device while acting as the observer network device; and determine the position of the target device further based on the second timing information.
 23. A method of determining a position of a target device, the method comprising: sending a first instruction to a first network device to act as a measurement network device to send a first measurement signal; sending a second instruction to a second network device to act as an observer network device to receive the first measurement signal, the first network device having a first known position and the second network device having a second known position; receiving first timing information associated with the first measurement signal; and determining the position of the target device based on the first timing information, the first known position, and the second known position.
 24. The method of claim 23 wherein: the first timing information comprises: a transmission time of the first measurement signal; a first time of arrival in the first network device of a first acknowledgement signal sent by the target device in response to receiving the first measurement signal; a second time of arrival of the first measurement signal in the second network device; and a third time of arrival of the first acknowledgement signal in the second network device; and determining the position of the target device comprises determining a first distance and a second distance from the target device to the first network device and the second network device, respectively, using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival.
 25. The method of claim 24 wherein using the transmission time, the first time of arrival, the second time of arrival, and the third time of arrival comprises determining a difference between (1) a difference between the first time of arrival and the transmission time and (2) a difference between the third time of arrival and the second time of arrival.
 26. The method of claim 23 further comprising instructing a third network device to act as another observer network device, the third network device having a third known position, wherein: the first timing information further comprises: a fourth time of arrival of the first measurement signal in the third network device; and a fifth time of arrival of a first acknowledgement signal in the third network device; and determining the position of the target device comprises determining a third distance from the target device to the third network device using the fourth time of arrival and the fifth time of arrival.
 27. The method of claim 23 further comprising: instructing the first network device to act as the observer network device and the second network device to act as the measurement network device; and receiving second timing information associated with a second measurement signal sent from the second network device and received by the first network device while acting as the observer network device; wherein determining the position of the target device is further based on the second timing information. 